CVE-2021-29484 is a medium-severity (CVSS 6.8) Cross-site Scripting (XSS) vulnerability in ghost. 1 public exploit reference exists, so weaponization risk is real. A fix is available for ghost — see the affected versions and patch details below.
DOM XSS in Theme Preview
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-29484 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
ghostnpmDescription
Impact
An unused endpoint added during the development of 4.0.0 has left sites vulnerable to untrusted users gaining access to Ghost Admin. Attackers can gain access by getting logged in users to click a link containing malicious code. Users do not need to enter credentials and may not know they've visited a malicious site.
Ghost(Pro) has already been patched. We can find no evidence that the issue was exploited on Ghost(Pro) prior to the patch being added.
Self-hosters are impacted if running Ghost a version between 4.0.0 and 4.3.2. Immediate action should be taken to secure your site - see patches & workarounds below.
Patches
Fixed in 4.3.3, all 4.x sites should upgrade as soon as possible. As the endpoint is unused, the patch simply removes it.
Workarounds
- Log out of Ghost Admin
- Suspend any users who cannot log out
- Block access to
/ghost/preview
Example of how to block access in nginx:
location ~ /ghost/preview {
rewrite ^(\/(.*\/)?ghost\/)(.*)$ $1 redirect;
}
This redirects the endpoint to /ghost/, which mimics the behaviour after the patch is applied.
References
For more information
If you have any questions or comments about this advisory:
- email us at [email protected]
Credits: Paul Gerste, SonarSource (https://www.sonarsource.com/)
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | ghost | ≥ 4.0.0&&< 4.3.3 | 4.3.3npm install ghost@4.3.3 |
Affected Products
ghostghostResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for ghost, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update ghost to 4.3.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-29484 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
How to detect CVE-2021-29484
A community-maintained Nuclei template exists for this CVE. You can scan for it directly:
nuclei -id cve-2021-29484 -u https://target- Template
- Ghost CMS <=4.32 - Cross-Site Scripting
- Severity
- medium
- Impact
- Successful exploitation of this vulnerability could allow an attacker to execute arbitrary JavaScript code in the context of the victim's browser, leading to potential data theft, session hijacking, or defacement of the affected website.
- Remediation
- This issue has been fixed in 4.3.3.
Template by ProjectDiscovery nuclei-templates (rootxharsh, iamnoooob), MIT licensed. View the full template. Scan only systems you are authorised to test.
Frequently Asked Questions
Is CVE-2021-29484 in your dependencies?
Find it across npm, including transitive dependencies.